The invention relates to a mobile radio station comprising means for synchronization with data streams transmitted by base stations of a cellular mobile radio system over radio channels.
GSM mobile radio systems (Global System for Mobile communications) comprise a network of radio cells. But each radio cell has a base station which radiates radio signals for mobile radio stations located in such a radio cell, a data traffic between a base station and mobile radio stations being effected over radio channels while use is made of the TDMA multiplex technique (Time Division Multiple Access). If a user of a mobile radio station moves with his station from one radio cell to a neighboring radio cell, there is to be ensured that a bidirectional radio link to at least one base station is available without interruptions, with a quality sufficient for an error-free data exchange. For this purpose, a mobile radio station in operation monitors all the available RF channels (Radio Frequency radio channels) of the mobile radio system (compare GSM 05.08, DRAFT pr ETS 300 578, March 1995, Second Edition, to which also the following state of the art implementations relate; when other parts of the GSM recommendations are cited in the following, also the respective version, dated March 1995, is meant). During this monitoring operation, the receiving levels of the RF channels are measured and an average receiving level is determined from a plurality of measured receiving levels of an RF channel. For a cell selection or cell reselection, i.e., for setting up a connection to the base station of such a radio cell, the mobile station is to be in a position to synchronize with the carrier frequency of a so-termed BCCH (Broadcast Control Channel) transmitted by the base station, and to read BCCH data. BCCH data contain system information and the so-termed BSIC (Base Transceiver Station Identity Code, Base Station Transceiver Code). A radio cell selected in this way is called a serving cell. In accordance with the standardized GSM recommendations, a mobile radio station is to try at least every thirty seconds to decode the BSIC of a serving cell. Furthermore, a mobile radio station is expected to verify at least every 30 seconds the BSIC of the other radio cells having the highest average receiving level. The BSIC is transmitted over the BCCH in signal beams by means of Synchronization Bursts (SB). A so-termed cell change function is carried out in which the function of serving cell changes to another radio cell based on the evaluation of the receiving level and the evaluation of the BSIC.
The operations of synchronization with a BCCH carrier frequency and of the decoding of a BSIC, require energy and form a load on the energy store of a mobile radio station. As a rule, accumulators are used as energy stores. Especially with mobile radio stations, this is a critical item. The smaller the energy consumption when a mobile radio station is operated, the longer such a mobile radio station can be operated, until a renewed charging of the accumulator is necessary, so that the user's convenience is enhanced.